The invention relates to a traction device for heat-sensitive ink ribbons as those used for marking surfaces, of the type which allow to fully employ the heat-sensitive ink ribbon, as currently devices are available in which unused ribbon segments are left between one marking and another. For this purpose the invention intends to use these segments by rewinding the ribbon using a simple and inexpensive device.
The invention is applicable to any type of marking with heat-sensitive ink ribbons, such as in marking plastic film with barcodes or other types of data.
There exist in the present state of the art well-known devices for traction of heat-sensitive ink ribbon which comprise a cylinder of origin of the heat-sensitive ink ribbon which is guided by small rollers to a rewinding cylinder, which is related to a traction mechanism. In the path of the ribbon is provided at least one marking head, so that between markings as the ribbon advances there is a segment of ribbon left unused.
These type of devices have the disadvantage of wasting a large amount of heat-sensitive ink ribbon.
To solve this drawback a system is known which allows to rewind the ribbon so that marking is allowed using the ribbon segments which run between markings, for which means are provided which allow the rewinding cylinder to rotate in the sense opposite the advance sense. These means include two shafts, each related to a motor, which drive the ribbon when the rewinding cylinder is turned in said opposite sense, thereby allowing the ribbon to move backwards. This system requires to install additional motors and a precise electronic control, so that it is a sophisticated system with a high cost.
To achieve the aforementioned objectives the invention has developed a novel traction device for heat-sensitive ink ribbon which allows to use the entire ribbon, by means of a simple and inexpensive device.
With this purpose the device of the invention includes novel means for rewinding and tensioning the ribbon, characterised in that they include a moving support provided with guiding means for the ribbon, so that the ribbon executes an additional motion. In addition means are provided which brake the cylinder of origin so that when the ribbon is driven in the forward direction with the origin cylinder braked, the ribbon makes the support advance against the action of an elastic element which complements said support, thereby reducing the additional path traveled by the ribbon, so that after marking the driving means force a backwards motion of the ribbon. This backwards motion implies that the support moves back under the action of the elastic element, to place the marking head in a segment prior to the end of the marking already performed, equivalent to the space traveled by the ribbon during the time taken by the header to descend when making another mark. Thus, when this new mark is made the header will meet the ribbon just after the last marking performed, so that the entire ribbon is used in the marking.
In this manner the forwards-backwards motion of the ribbon does not affect in any way the cylinder of origin, which remains braked, thus greatly simplifying the forwards-backwards motion of the ribbon.
The braking means for the origin cylinder are driven by the moving support, so that after performing one or several markings with the corresponding advances and returns the support will release the braking means, to unroll a length of ribbon as requested by the traction means in a forward direction.
The braking means of the cylinder of origin acts when the moving support reaches a set advance position in which in contacts said braking means and these release the cylinder of origin. Thus while maintaining the advance of the traction means, the ribbon is unrolled by successive brakings-releases of the origin cylinder. Afterwards the traction rotation is inverted making the support return due to the action of the spring, so that the origin cylinder is again locked.
The entire process is repeated successively, and all while maintaining the ribbon tense by means of the elastic element which aids the moving support.
In order to attain this functionality the braking means of the origin cylinder are determined by a swivelling lever aided by a spring provided with a shoe, so that the spring keeps the shoe presses against the shaft of the origin cylinder.
The lever is placed in the path of the support, so that when the support contacts with it the lever swivels against the action of the spring, causing the release of the origin cylinder. This situation allows unwinding of the origin cylinder when the ribbon is tractioned.
The elastic element which complements the support is a spring. Said support is retained in guides in which it slides during its forward and backward motion.
Additionally, a stop is provided which limits the run of the support during its backwards motion, in order to ensure the correct operation of the device.
The guide means for the ribbon provided in the support consist of a cylinder which aids the advance and return of the ribbon.
These and further characteristics of the invention will be made apparent in view of the accompanying drawings, where for purposes of illustration only the following is shown.